The present invention is directed to improvement of free-ink collector type writing instruments, such as ball-point pens, felt tip pens, fountain pens and the like, having a writing tip as a writing element at the front end thereof, an ink tank for directly storing ink and a collector as a regulator for regulating the inner pressure by making use of capillary effect. In particular, the present invention relates to improvement against the problem of ink leakage from the writing tip due to frozen ink in freezing cold and while in use on an airplane and against the problem of natural ink flow-out.
There have been conventionally known writing instruments which have a collector between the point assembly and the ink tank for the purpose of keeping free-state ink by regulating the pressure inside the ink tank so as to prevent ink leakage from the writing tip and ink flooding through the air vent. The collector type writing instruments delivers an ample amount of ink equivalent to or greater than the initial state of sliver-type writing instruments, and have the advantages in that thick drawn lines can be drawn with little writing pressure without any gradual reduction in ink delivery until ink exhaustion, the ability to load an ample amount of ink, the ability of monitoring the remaining amount of free ink and other features.
However, the collector type writing instrument has the drawback that it has to be designed taking into consideration the problem of ink flooding, which might occur when increase and reduction in air pressure resulting from variations in temperature and pressure and change in height repeatedly occur. Conventionally, collector type writing instruments have been considered to be almost perfect if they can be used from room temperature about 20xc2x0 C. to 50xc2x0 C., which is the conceivable maximum temperature of the air. However, the problem of forward leakage, i.e., ink leakage from the pen tip, resulting from sharp increase and decrease in pressure when the pen is used on an airplane or resulting from a volume expansion occurring due to frozen ink under a storage environment in winter, e.g., xe2x88x9220xc2x0 C. in arctic areas such as Northern Europe, Canada and the like, has come to be known.
This forward leakage problem due to freezing has, conventionally, been handled by increasing the amount of an antifreeze solution to the ink or by using special elements such as a tip rubber seal for the writing tip. Attempts to solve the problem with ink, in most cases, result in adverse influences on safety, drying performance of drawn lines, ink stability and the like. On the other hand, the attempt to solve the problem with a rubber seal, not only increases the parts cost and assembly cost but also causes a problem of the tip being constantly stained with ink by the rubber seal.
In order to solve this forward leakage problem, the applicant hereof has already proposed an invention disclosed in Japanese Patent Application Laid-open Hei 11 No. 334276 and others. In this invention, the forward leakage problem from the writing tip is solved by leading ink which is pushed out by volume expansion due to frozen ink at a temperature below 0xc2x0 C. or sharp increase in temperature, from the collector interior to the collector exterior.
A collector type writing instrument is configured so that ink inside the ink tank is put into contact with an air exchanger hence the air exchanger is wetted with ink and the interior is isolated from the outside air other than at the air exchanger whereby ink or air is exchanged only through the air exchanger which presents a strong enough capillary attraction. Thus, the collector type writing instrument is a writing instrument using the mechanism that the meniscus created by the strong capillary attraction from the air exchanger, in effect, reduces the pressure inside the ink tank so that no ink will flow out from the tip of the point assembly when the tip is down.
As already mentioned in the preceding application, there has been known a defect. That is, once ink components leak out from the writing tip because of volume expansion due to freezing, they will never return from the writing tip after thawing, and are left as they have been spilt. Further, it was found that this freezing problem could be solved by providing a passage hole in the collector.
However, the preceding application only provides a simple passage hole, so that the following problems occur. That is, when the writing instrument is used under a high temperature high humidity environment or when the writing instrument has been left on a pen holder over long time with its pen tip down, ink oozes out from the passage hole over the passage of time, staining its appearance, or in the worst case, the collector retaining grooves below the passage hole alone are filled up with ink, causing ink to flood out through the air hole. There is also an exudation problem that ink spontaneously oozes and spreads out through the passage hole from the internal ink feed such as an pen core as an ink feeder portion.
Further, it was also found that when the writing instrument is used under a condition in which a sharp change in pressure occurs such as on an airplane, the pressure on the ink tank side acts on the ink and causes the ink to directly flood out in rush through both the air/liquid exchanger and passage hole, whereby ink flows out without making efficient use of the collector""s surplus ink retaining function.
It is therefore an object of the present invention to make improvement of collector type writing instruments of a popular type. That is, it is an object to meet the demands for improvement of writing instruments in their accident prevention capabilities such as prevention against ink leakage caused by increase and decrease in the inner pressure of the ink tank resulting from change in temperature and change in air pressure and the like, prevention against ink flooding and forward leakage when they are stored at shops for long time and prevention against ink leakage due to freezing, to avoid crucial accidents such as pollution of consumer""s clothes and to solve the above problems without degrading the excellent writing performance of the conventional collector type writing instruments without increase in cost.
The collector type writing instrument of the present invention to attain the above object is comprised of an ink feeder portion using the capillary attraction of an ink feed core (center core, collector core, collector itself with a slit, or the like) for assuring the flow path of ink from an ink tank to a writing point and a collector disposed between the ink tank of a cup-like shape having a bottom and the writing point for regulating the inner pressure by holding surplus ink utilizing capillary effect, and the examples include ball-point pens, felt-pens in which an ink feed core itself serves as a writing point, markers, fountain pens, small-tube writing instruments and the like.
In general, the collector has a vent portion connected to the outside air, a collector air groove and an air/liquid exchanger capable of allowing ink and air to move between the collector and the ink tank and capable of holding ink by a capillary attraction and is constructed so that air will not enter the ink tank except through the air/liquid exchanger by wetting the collector air/liquid exchanger. A typical collector is composed of a long narrow ink groove and a plurality of vanes radially arranged at appropriate intervals forming gaps or retaining grooves therebetween, so as to provide the function of regulating the inner pressure inside the writing instrument body by allowing ink to move into and out of the retaining grooves. Other than the above, a sliver made up of a fiber bundle, sponge may be used as a collector by subjecting it to an appropriate wettability adjusting treatment.
The first effective means of the present invention is characterized in that a passage hole is formed from the outer side surface of the collector toward the inner hollow of the collector, the passage hole being formed so as to present a smaller capillary attraction than that of the air/liquid exchanger and that of the feeder portion such as a center core. Simply, this configuration is constructed so that no ink will be drawn out from the collector inner hollow toward the outer side surface.
The reason why the capillary attraction of the passage hole is set to be smaller than that of the air/liquid exchanger is that if the capillary attraction of the passage hole is greater, ink is liable to move through the air/liquid exchanger when a sharp increase or decrease in pressure inside the ink tank occurs, hence the passage hole cannot be used efficiently, which easily leads to occurrence of ink flooding, ink leakage and other deficiencies. Reduction of the capillary attraction of the passage hole smaller than that of the feeder portion can be performed by enlargement of the passage hole, elimination of acute portions from the corners of the passage hole, elimination of grooves and projections in the interior wall of the passage hole and other methods.
Next, the effective means for supporting the first means will be itemized hereinbelow. The second effective means is characterized in that, in addition to the above means, the passage hole presents a smaller capillary attraction on the outer surface side of the collector than that on the inner surface side. Illustratively, the passage hole is constructed in a tapered configuration in which the bore diameter becomes greater from the inner side of the collector (on the inner hollow side) toward the outer side (outer side surface) or by making the curvature R of the corners on the inner side greater than that on the outer side.
The third effective means is characterized in that the collector is comprised of a plurality of vanes defining retaining grooves capable of holding surplus ink, and the passage hole is formed at one retaining groove located at a position more rearwards and closer to the ink tank side than the front most retaining groove (preferably at a retaining groove located more rearwards, by skipping one or more grooves, from the front most one to the ink tank side).
The fourth effective means is characterized in that a clearance presenting a capillary attraction smaller than that of the air/liquid exchanger and greater than that of the passage hole is formed around the passage opening on the inner hollow side, between the collector inner wall and the feeder portion. In the case where the collector inner hollow incorporating the feeder portion is comprised of a small-diametric portion and a large-diametric portion located on the tip side, more frontward than the small-diametric portion, the following relationship between the strengths of capillary action can be created: (air/liquid exchanger) greater than (gap at the small-diametric portion) greater than (gap at the large-diametric portion) greater than (passage hole).
The fifth effective means is characterized in that the surface of the passage hole is formed so as to present less wettability with ink than the other part of the collector, by providing a different surface roughness, a different surface treatment or construction with a different material, from that of the other part of the collector. This configuration also provides the function of preventing ink leakage, similarly to the above configurations.
The transparent or translucent ink tank made up of synthetic resin for directly holding ink has the collector press-fitted therein so that ink will not leak out. The ink should contain 40% or more water or solvent as its base and have a relatively low viscosity of 2 to 100 mpaxc2x7s at normal temperature. There are different types of ink: dye ink which can be dissolved in the main solvent; and pigment ink in which as water resistant, light stable coloring agents, pigments such as carbon black, pseudo-organic pigments such as color-coated resin powders, aluminum or other metal powders, inorganic substances such as titanium oxide, mica, or glass fragments and the like, are dispersed. Ink which has been used in the conventional collector type writing instruments can be used. Ink is not particularly limited in the present invention, but ink which is based on an organic solvent such as alcohols, xylene, etc., can also be used for the present invention as long as it can provide the function of a collector type writing instrument.